Numerically controlled machine tools which operate only about X-, Y-, and Z-axes have a cutter axis that is oriented always in a vertical direction, i.e., in any of the axis directions. If two rotational axes are added to such a numerically controlled machine tool, making it a 5-axis numerically controlled machine tool, then the cutter axis may be oriented in any optional direction. For example, a 5-axis diesinking machine can machine a workpiece three-dimensionally with a cutter that can be tilted in any optional direction.
A process of three-dimensionally machining a workpiece with a cutter includes a mode in which the cutter is tilted and the workpiece is machined by an edge of the cutter. In such a mode, a cutter compensation vector is required to be determined as a three-dimensional vector. Heretofore, there have been available different methods of determining a cutter compensation vector as a three-dimensional vector.
According to the first method, an automatic programming apparatus is used to calculate a cutter compensation vector. When the automatic programming apparatus generates a machining program, it simultaneously calculates a cutter compensation vector for automatically determining a cutter path which has been compensated for.
The second method relies upon an NC programmer to calculate the tilt of a cutter, an amount of compensation, and a direction of compensation when a machining program is generated.
The first method which employs an automatic programming apparatus has the following problems: Since the first method needs an automatic programming apparatus at all times, the overall system is expensive. Therefore necessary for the automatic programming apparatus to generate a machining program each time the cutter radius changes.
The second method in which calculations are carried out by an NC programmer is also disadvantageous for the following reasons: When a workpiece surface to be machined varies, i.e., when a curved surface is to be machined, a very large number of calculations is required, and program commands are highly complex, resulting in a large expenditure of time and labor to generate a machining program.
The above methods of determining a cutter compensation vector are also more complex if the cutter has a round edge as with an end mill.